Message-ID: <ca590101-bfc8-3934-d803-537aacb707e0@huawei.com>
Date:   Wed, 11 Sep 2019 14:15:51 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Greg KH <gregkh@...uxfoundation.org>, <rafael@...nel.org>,
        <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <mingo@...nel.org>, <linuxarm@...wei.com>
Subject: Re: [PATCH] driver core: ensure a device has valid node id in
 device_add()

On 2019/9/11 13:33, Michal Hocko wrote:
> On Tue 10-09-19 14:53:39, Michal Hocko wrote:
>> On Tue 10-09-19 20:47:40, Yunsheng Lin wrote:
>>> On 2019/9/10 19:12, Greg KH wrote:
>>>> On Tue, Sep 10, 2019 at 01:04:51PM +0200, Michal Hocko wrote:
>>>>> On Tue 10-09-19 18:58:05, Yunsheng Lin wrote:
>>>>>> On 2019/9/10 17:31, Greg KH wrote:
>>>>>>> On Tue, Sep 10, 2019 at 02:43:32PM +0800, Yunsheng Lin wrote:
>>>>>>>> On 2019/9/9 17:53, Greg KH wrote:
>>>>>>>>> On Mon, Sep 09, 2019 at 02:04:23PM +0800, Yunsheng Lin wrote:
>>>>>>>>>> Currently a device does not belong to any of the numa nodes
>>>>>>>>>> (dev->numa_node is NUMA_NO_NODE) when the node id is neither
>>>>>>>>>> specified by fw nor by virtual device layer and the device has
>>>>>>>>>> no parent device.
>>>>>>>>>
>>>>>>>>> Is this really a problem?
>>>>>>>>
>>>>>>>> Not really.
>>>>>>>> Someone need to guess the node id when it is not specified, right?
>>>>>>>
>>>>>>> No, why?  Guessing guarantees you will get it wrong on some systems.
>>>>>>>
>>>>>>> Are you seeing real problems because the id is not being set?  What
>>>>>>> problem is this fixing that you can actually observe?
>>>>>>
>>>>>> When passing the return value of dev_to_node() to cpumask_of_node()
>>>>>> without checking the node id if the node id is not valid, there is
>>>>>> global-out-of-bounds detected by KASAN as below:
>>>>>
>>>>> OK, I seem to remember this being brought up already. And now when I
>>>>> think about it, we really want to make cpumask_of_node NUMA_NO_NODE
>>>>> aware. That means using the same trick the allocator does for this
>>>>> special case.
>>>>
>>>> That seems reasonable to me, and much more "obvious" as to what is going
>>>> on.
>>>>
>>>
>>> Ok, thanks for the suggestion.
>>>
>>> For arm64 and x86, there are two versions of cpumask_of_node().
>>>
>>> when CONFIG_DEBUG_PER_CPU_MAPS is defined, the cpumask_of_node()
>>>    in arch/x86/mm/numa.c is used, which does partial node id checking:
>>>
>>> const struct cpumask *cpumask_of_node(int node)
>>> {
>>>         if (node >= nr_node_ids) {
>>>                 printk(KERN_WARNING
>>>                         "cpumask_of_node(%d): node > nr_node_ids(%u)\n",
>>>                         node, nr_node_ids);
>>>                 dump_stack();
>>>                 return cpu_none_mask;
>>>         }
>>>         if (node_to_cpumask_map[node] == NULL) {
>>>                 printk(KERN_WARNING
>>>                         "cpumask_of_node(%d): no node_to_cpumask_map!\n",
>>>                         node);
>>>                 dump_stack();
>>>                 return cpu_online_mask;
>>>         }
>>>         return node_to_cpumask_map[node];
>>> }
>>>
>>> when CONFIG_DEBUG_PER_CPU_MAPS is undefined, the cpumask_of_node()
>>>    in arch/x86/include/asm/topology.h is used:
>>>
>>> static inline const struct cpumask *cpumask_of_node(int node)
>>> {
>>>         return node_to_cpumask_map[node];
>>> }
>>
>> I would simply go with. There shouldn't be any need for heavy weight
>> checks that CONFIG_DEBUG_PER_CPU_MAPS has.
>>
>> static inline const struct cpumask *cpumask_of_node(int node)
>> {
>> 	/* A nice comment goes here */
>> 	if (node == NUMA_NO_NODE)

How about "(unsigned int)node >= nr_node_ids", this is suggested
by Peter, it checks the case where the node id set by fw is bigger
or equal than nr_node_ids, and still handle the < 0 case, which
includes NUMA_NO_NODE.

Maybe define a macro like below to do that in order to do
the node checking consistently through kernel:

#define numa_node_valid(node)	((unsigned int)(node) < nr_node_ids)


>> 		return node_to_cpumask_map[numa_mem_id()];
>>         return node_to_cpumask_map[node];
>> }
> 
> Sleeping over this and thinking more about the actual semantic the above
> is wrong. We cannot really copy the page allocator logic. Why? Simply
> because the page allocator doesn't enforce the near node affinity. It
> just picks it up as a preferred node but then it is free to fallback to
> any other numa node. This is not the case here and node_to_cpumask_map will
> only restrict to the particular node's cpus which would have really non
> deterministic behavior depending on where the code is executed. So in
> fact we really want to return cpu_online_mask for NUMA_NO_NODE.

>From below, if the __GFP_THISNODE is set, the fallback is not performed.
For node_to_cpumask_map() case, maybe we can return the cpumask that is
on the node of cpu_to_node(raw_smp_processor_id()) for NUMA_NO_NODE,
because the current cpu does belong to a node, and the node does have at
least one cpu, which is the cpu is calling the node_to_cpumask_map().

Make any sense?

/*
 * Allocate pages, preferring the node given as nid. The node must be valid and
 * online. For more general interface, see alloc_pages_node().
 */
static inline struct page *
__alloc_pages_node(int nid, gfp_t gfp_mask, unsigned int order)
{
	VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES);
	VM_WARN_ON((gfp_mask & __GFP_THISNODE) && !node_online(nid));

	return __alloc_pages(gfp_mask, order, nid);
}

> 
> Sorry about the confusion.
>> -- 
>> Michal Hocko
>> SUSE Labs
> 

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